Production of high strength steel structural shapes



United States Patent 3,117 ,037 PRODUCTION OF HIGH STRENGTH STEELSTRUCTURAL SHAPES John M. Hodge, Pleasant Hills, Pa., assignor to UnitedStates Steel Corporation, a corporation of New Jersey No Drawing. FiledSept. 22, 1961, Ser. No. 139,871 5 Claims. (Cl. 14812.3)

This invention relates to the production of structural steel shapesformed of high strength steel and more particularly to a method offorming straight, high strength, steel structural shapes.

In many structures such as bridges, towers, transportation and storageequipment there is a need for structural shapes having high strength. Ifstructural shapes, such as beams, channels and angles having yieldstrengths in excess of 80,000 p.s.i. were available, a considerablereduction in weight could be obtained in such structures and alongtherewith reduced costs. Heretofore many attempts have been made toproduce high strength in such structural shapes by resorting toconventional quenching and tempering. That is to say the high strengthswere produced by drastically quenching the shapes formed of hardenablesteel from an austenitizing temperature. While desired mechanicalproperties can be so obtained, the abrupt transformation or change inmicrostructure produces distortion so that the shapes have excessivecamber, sweep, or twist or other distortion defects. Due to the highstrength of such shapes, straightening by conventional straighteningmethods is very uneconomical and diflicult and moreover has adeleterious effect on the mechanical properties of the steel.

It is accordingly an object of the present invention to produceundistorted and straight structural shapes of high strength steel.

It is a further object to produce such shapes in an efiicient andeconomical manner.

I have discovered a method of producing structural shapes havingstrengths and properties comparable to quenched and tempered shapes andwhich are within commercial straightness tolerances. Successfulutilization of the method of my invention requires the use of alow-carbon steel having a sufiiciently high hardenability that it willobtain the desired hardness air cooling on a conventional hot-bed. Steelwithin the following compositional limits is satisfactory for practicingmy invention:

Percent Carbon .15/ .20 Manganese .20/ .50 Silicon .15/ .35 Nickel250/425 Chromium 1.30/2.00 Molybdenum .35/ .55

with the balance iron, residual impurities and other elements in amountswhich do not deleteriously affect the properties.

Within such ranges, I have two preferred compositions as follows:

Table 1 Carbon .15/.20 Manganese flicon. Nickel. Chrorni M olybdenumbalance iron and residual impurities.

In accordance with my invention, structural shapes are "ice rolled fromsuch steels by conventional practice and while at hot-rollingtemperatures and in an austenitic condition are straightened, preferablyby roller straightening, directly folowing the hot-rolling. Afterstraightening while in an austenitic condition the shapes are placed onconventional hot-beds and cooled to room temperature. During cooling,the steel transforms to a structure of lower bainite and martensite andbecause of the slow cooling rate is essentially straight due to lack ofdistortion during cooling and transformation. Any slight distortions atthis stage can easily be removed by gagpress or the like straightening.However, the cooling rate is sufficiently fast to produce a structure oflower bainite and martensite. Following transformation on the hotbed,the sections have the desired high strength but due to the presence ofmartensite may be lacking in toughness so that I prefer a finaltempering step.

As an example of my invention, I have produced structural sections ofsteel of the following composition:

Percent Carbon .15 Manganese .26 Silicon .25 Nickel 2.95 Chromium 1.83Molybdenum .48

After hot-rolling, the sections Were roller-straightened, cooled on ahot-bed to room temperature and thereafter tempered at 1225 F. Thesections were straight within commercial tolerances. Mechanicalproperties of three different sections so produced were as follows:

As can be seen, these properties are equivalent to those obtained byquenching and tempering, including high strength and toughness.Moreover, the sections were straight Within commercial tolerances asproduced.

While I have shown and described several specific embodiments of myinvention, it will be understood that these embodiments are merely forthe purpose of illustration and description and that various other formsmay be devised within the scope of my invention, as defined in theappended claims.

I claim:

1. A method of producing high strength steel structural sections such asbeams, channels and angles comprising hot-rolling sections of low-carbonsteel having sufliciently high hardenability that it will harden duringair cooling on a hot-bed, straightening said sections after hot-rollingand prior to cooling below the temperature at which the steel isaustenitic, air cooling said sections to room temperature on a hot-bedat a rate sufficiently slow that distortion due to abrupt transformationdoes not occur but at a rate sufliciently fast to produce amartensitic-bainitic structure therein and thereafter tempering saidsections at a temperature below the lower critical temperature thereof.

2. A method of producing high strength steel structural sections such asbeams, channels and angles comprising forming sections of steel of thefollowing composition:

Percent Carbon .15/ .20 Manganese .20/ .50 Silicon .15/ .35

Nickel 2.50/425 Chromium 130/200 Molybdenum .35/ .55

with the balance iron, residual impurities and other elements in amountswhich do not deleteriously affect the properties, straightening saidsections after hot-rolling and before cooling below an austenitizingtemperature, air cooling the straightened sections at a cooling ratesufficiently slow to prevent distortion therein but at a ratesufficiently fast to produce a transformation of the structure of thesteel to lower bainite and martensite and thereafter tempering thesections at a temperature below the critical temperature thereof.

3. A method of producing high strength steel structural sections such asbeams, channels and angles comprising forming sections of steel of thefollowing composition:

Percent Carbon .15/ .20

Manganese .20/ .45 Silicon .15/ .30

Nickel 2.75/3.25

Chromium 1.60/ 1.90

Molybdenum .40/ .60

balance iron and residual impurities, roller straightening said sectionsafter hot-rolling and before cooling below an austenitizing temperature,air cooling the straightened sections on a hot-bed at a cooling ratesufiiciently slow to prevent distortion therein but at a ratesuificiently fast to produce a transformation of the structure of thesteel to lower bainite and martensite and thereafter tempering thesections at a temperature below the critical temperature thereof.

4. A method of producing high strength steel structural sections such asbeams, channels and angles comprising forming sections of steel of thefollowing composition:

Percent Carbon .15/ .20 Manganese .20/ .45 Silicon .15/ .30 Nickel3.75/4.25 Chromium 1.75/2.00 Molybdenum .40/ .65

balance iron and residual impurities, roller straightening said sectionsafter hot-rolling and before cooling below an austenitizing temperature,air cooling the straightened sections on a hot-bed at a cooling ratesufliciently slow to prevent distortion therein but at a ratesufficiently fast to produce a transformation of the structure of thesteel to lower bainite and martensite and thereafter tempering thesections at a temperature below the critical temperature thereof.

5. A method of producing high-strength structural shapes such as beams,channels and angles comprising hot-rolling structural shapes from steelcontaining Percent Carbon About .15 Manganese About .26 Silicon About.21 Nickel About 2.95 Chromium About 1.83. Molybdenum About .48

with the balance iron and residual impurities, hot-roller straighteningsaid sections at the finish of the hot-rolling and before the sectionshave cooled below an austenitizing temperature, air cooling saidsections on a hot-bed to produce straight sections having a lowerbainite, martensitic structure therein and then tempering said sectionsat a temperature of about 1225 F.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, ll7037 January 7, 1964 John M, Hodge corrected below.

Column 1 line 44, afte r "hardness?! insert --.durin'g column 4, line 6,for "1,75/

200" read 1. 70/2000 Signed and sealed this 26th day of May 1964..

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. A METHOD OF PRODUCING HIGH STRENGTH STEEL STRUCTURAL SECTIONS SUCH ASBEAMS, CHANNELS AND ANGLES COMPRISING HOT-ROLLING SECTIONS OF LOW-CARBONSTEEL HAVING SUFFICIENTLY HIGH HARDENABILITY THAT IT WILL HARDEN DURINGAIR COOLING ON A HOT-BED, STRAIGHTENING SAID SECTIONS AFTER HOT-ROLLINGAND PRIOR TO COOLING BELOW THE TEMPERATURE AT WHICH THE STEEL ISAUSTENITIC, AIR COOLING SAID SECTIONS TO ROOM TEMPERATURE ON A HOT-BEDAT A RATE SUFFICIENTLY SLOW THAT DISTORTION DUE TO ABRUPT TRANSFORMATIONDOES NOT OCCUR BUT AT A RATE SUFFICIENTLY FAST TO PRODUCE AMARTENSITIC-BAINITIC STRUCTURE THEREIN AND THEREAFTER TEMPERING SAIDSECTIONS AT A TEMPERATURE BELOW THE LOWER CRITICAL TEMPERATURE THEREOF.